210 EXCRETION BY THE KIDNEYS AND SKIN 



losum, (4) the rete mucosum or Malpighii. All these except the 

 stratum corneum have a fairly constant thickness. The stratum 

 corneum is thick or thin according to location and degree of 

 exposure, and its cells are flat and horny. The lowest cells of 

 the rete mucosum are columnar. From this last-named layer 

 the cells pass gradually upward, and as gradually assume the 

 shape of the horny layer. The horny cells are thrown off and 

 their place is taken by others from beneath. (Fig 60.) 



Hairs are to be found on almost all parts of the cutaneous 

 surface. They consist of a bulb and a shaft. A depression of 

 the skin involving both epidermis and cutis vera constitutes the 

 hair-follicle in which the bulb rests. A projection at the bottom 

 of the follicle corresponds to a papilla, and upon it the bulb is 

 placed. The shaft has an oval shape in cross section. It is com- 

 posed of fibrous tissue, outside which is a layer of imbricated 

 cells. 



Nails consist of a superficial layer of horny cells and a deeper 

 one corresponding to the rete mucosum. The root of the nail 

 is received into the matrix a specialized portion of the cutis 

 vera. 



Cutis Vera. The cutis vera is tough but elastic. It rests 

 upon cellular and adipose tissue. Its structure is areolar with 

 some non-striated muscle fibers. Projecting from the cutis vera 

 into the epidermis are minute conical elevations, the papilla. 

 Many of them contain sensory nerve terminals. 



Sweat Glands. Practically the whole cutaneous surface con- 

 tains sweat glands. Some two and a half millions are thought to 

 exist in the skin of the average individual. They are particularly 

 abundant in the skin of the palms of the hands and soles of the 

 feet. They belong to the simple tubular type, and consist of a 

 secreting portion and an excretory duct. The secreting part lies 

 just underneath the true skin and, as a whole, resembles a small 

 nodule; however, the nodule consists of an intricate coiling of the 

 tube itself which is of approximately uniform diameter throughout. 



